Electricians who have served their time etc are as accountable for their actions as those who have no formal training. Anyone can be an 'electrician', so lets not blow the trade out of proportion. Domestic wiring is easy, but we like the idea of DIYers thinking its complicated. I'm just setting the record straight.
Plumbing = pump, manifold, pressure relief valves, pipework (flow & return), valves ...
Electrics = generator, distribution board, MCBs, cables (live & neutral), switches ...
Water (current) flows and if you squeeze the pipe then you increase the resistance and the water pressure rises. If the pipe is too small (1.5mm wire for a cooker supply) then the pressure in the pipe also increases and may burst.
Its no more than V=IR, P=VA, current carrying capacity and common sense. I run a course in my local college which teaches students domestic installation in 10 days. I could do it in 5 but I drag it out for greenbacks. And yes, I am a h*ll of a guy!!!